A monochromatic red (R), green (G), and blue (B) light source having well color balanced white light output is a very desirable light source for many display applications, because it is known to be more efficient compared to other conventional incoherent "white light" light sources with red, green and blue filters. For example, used in conjunction with 3 channel, transmissive Liquid Crystal Display (LCD) panel modulator based projection display systems, the monochromatic R,G,B light source producing well color balanced white light can achieve at least 4 times higher optical efficiency than conventional high intensity incoherent light sources, such as Xenon lamps or Metal Halide lamps with red, green and blue filters.
However, the monochromatic R,G,B light source has to originate from some sort of lasers producing a visible spectrum of red, green and blue. As a result, all the past attempts to develop such light sources have had the following shortcomings.
1. Use of some sort of gas lasers as light sources. This results in unacceptably low wall plug efficiency and constant need of laser maintenance.
2. Some of the 3 primary wavelengths generated by the R,G,B laser light sources may not be suited for display use.
3. Some spatial light modulators used in display applications work well with continuous wave (cw) R,G,B laser light sources. The others need pulsed R,G,B laser light sources. It has been known to be very difficult to generate suitable R,G,B colors efficiently from cw laser designs, and pulsed laser light sources in the past have not been suited to couple with spatial light modulators, which require cw light sources, due to unacceptable long pulse duration.
4. The final problem associated with past R,G,B laser light sources is laser speckle, this phenomenon is considered to be a random interference pattern of intensity, which results from the reflection or transmission of highly coherent light from (or through) an optically rough surface (one whose local irregularities in depth are greater than one quarter of a wavelength from a laser light source). The speckle is very annoying to look at, and past attempts employed to minimize the speckle have been to vibrate the screens to disturb phase coherency associated with each wavefront.